This invention relates to improvements in hydraulic systems for agricultural implements and to control and drive systems for same.
The demand for fluid power from tractors is increasing with the size of implements and with the increased use of hydraulic power on implements. Farm practices are becoming increasingly large and in order to complete seeding and preparations, there are demands for larger air seeding implements. Larger air seeder implements require more hydraulic power for hydraulically driven fans, augers, and other accessories. This demand may be more than the tractor can supply or leaves no reserve capacity to operate implement folding or lifting operations. The hydraulic accessories on the implement may also be a significant distance from the tractor hydraulic power source leading to power losses in long fluid lines and connections.
Separate hydraulic power systems have been used such as ground driven pumps but these have had separate fluid reservoirs, filters, and coolers, making the systems expensive. The Force V air seeder manufactured first by Friggstad Manufacturing and later by Flexi-Coil used a ground driven hydraulic pump to provide fluid power to the air seeder fan. The pump drive was achieved through a planetary gear system. Two pumps driven separately by two ground wheels were used in order to provide enough fluid power to drive the fin motor. Requirements for a fluid reservoir, cooling, filtration and the planetary gear drive added to the expense of the system. Other air seeders have used belts and pulleys to directly drive the fan from the ground wheels.
In all of these prior systems the fan speed was directly dependent on the speed that the implement was towed across the ground Inaccurate metering, delivery, and line plugging were problems with these prior systems.
An improved system used PTO (power take-off) driven pumps to provide fluid power to make up the shortcomings of the tractor hydraulics. ASAE paper 921604 describes such a hydraulic system. However, this is shown to separately provide power to implement actuators and is not shown to be combined with the tractor fluid power, except that the tractor provides a charge pressure to prevent cavitation of the PTO driven pump. The pump is shown to be tied into tractor hydraulics to make combined use of tractor hydraulic filter, reservoir, and cooling systems, but the high pressure fluid power delivered from the PTO pump is not shown to be connected in parallel with the high pressure from the tractor pump to operate implements together. The PTO pump system is sometimes in a location far from where the fluid power is required on an air seeder. Increased line sizes are required to avoid power losses and more connections and setup are required in order to use these systems.
It would be desirable to provide a hydraulic system on the implement which provides the extra power required without giving the operator further work and worry of connecting and setting up systems so they operate satisfactorily without significant loss in performance due to changing ground speeds, and a system which does not duplicate components already available on the tractor, thereby maintaining cost within reason.
A Design News article (issue date: Feb. 20, 1992), titled "PTO Driven Pump Augments Tractor Hydraulics" shows an auxiliary pump driven from a PTO drive and operating an implement motor. This circuit shows the tractor provides a charge pressure to the auxiliary pump limited by a relief shown on the tractor return line. The pressure available to the motor is not the combination of the tractor with the auxiliary pump but only the difference between the pressure provided by the auxiliary pump and the charge pressure because the charge pressure is also seen by the return side of the implement motor.